The move to a distributed architecture allows to significantly decrease design complexity of new mobile devices and as a result reduces time to market. Such a distributed architecture for a design in modular structure has been initiated by the Mobile Industry Processor Interface alliance (MIPI).
A key requirement of a device integrator is robustness and security of inter-device communications. Here, it is important to mention that the security threads are coming not only from “on purpose” violation of the internal rules, but also due to errors/misunderstanding created at the interface to the distributed architecture and on the layers above (applications). At the same time, cost is always a major factor for acceptance of the new technology.
A major issue at the present stage is the demand for the implementation of a simple and low cost security scheme in distributed network architectures on the mobile devices, which also increases their robustness. This demand is valid for the MIPI architecture, but also for a number of other distributed inter-device architectures such as “Discobus”, “Spacewire”, etc.
The robustness of a mobile device strongly depends on how secure the internal network of the components is, which implements the device functionality. It is especially important if the device should support the hot-plugin scenario, when the network has to identify how trustable the new nodes are. The current “Discobus” and “MIPI” proposals do not have an embedded security solution.
Although there is a broad range of prior art solutions in the area of network security (e.g. in the Internet), no prior art solution for the network types with the given features are yet known.
A further issue of the new distributed architecture is the datalink reliability of the bus technology of this distributed architecture. What has been suggested for this bus technology is a low power high-speed serial link bus designed to be a new kind of generic and modular bus well suited for portable terminals, but not limited to them. One example therefor is “Discobus” of the present Applicant which has many advantages compared to a traditional bus, such as that only few signals are needed, thus reducing the number of pins or balls on an IC package, and by consequence thus reducing the costs, that a much better electromagnetic compatibility (EMC) immunity is obtained, that it can replace many existing buses, because of its modularity and generality, and that it is hotpluggable.
As indicated above, what is now needed is a way of making a reliable datalink layer for this particular bus technology such as “Discobus” and the MIPI protocol stack specifications. The deployment of the reliable Datalink layer increases the network robustness and improves the reliability of the data transmission. Also the Datalink layer reliability in some cases de-facto can be seen as a way to provide the end-to-end (E2E) network reliability.
Specifically, present definitions of the bus technology do not necessarily contain a mechanism for providing the link level reliability. Lack of the Datalink layer reliability results in a need to create the E2E reliability schemes for all flow that require it, including different types of control and management traffic. There is an ongoing discussion among experts in the field whether the point-to-point reliability results in end-to-end reliability, but it is agreed that a bus that relies on the E2E reliability mechanism and does not have the link level reliability will significantly benefit from extending it with a new appropriate P2P reliability scheme.
Nowadays there is a number of P2P reliability solutions available, but the common problem is the traffic overhead created by the flow of acknowledgments. The standard way for decreasing the overhead is by grouping acknowledgments of multiple packets into a single acknowledgment message, however this approach does not solve the problem defined before, it just reduces its scale.
This problem becomes even more serious in the Quality of Service (QoS) aware networks, as the link level acknowledgments have to get at least the same level of service as the packets of the main flow. It requires to create an additional resource reservation for each link in the back direction, taking into account the worst-case scenario for acknowledgments (with smallest main flow packets granularity, and worst inter-arrival time). As a result the complexity of the resource reservation and management mechanisms is increasing dramatically, which in most cases leads to the network design errors.
A still further issue of the distributed architecture is related to the datalink layer scheme of acknowledgements. A current proposal implements the datalink layer reliability using a classical approach for providing End-to-End (E2E) reliability in the Internet. This method is based on a consistency analysis of the link level sequence numbers, which requires to reassign packet (frame) sequence numbers at each link. It also requires to re-compute a packet (frame) protection sequence (CRC) at each link. This method results in an increase of the datalink layer complexity and data overhead. Similar arguments are applicable to the currently used receiver (RX) buffer snapshot flow control mechanism, which transmits to the transmitter (TX) side information about the currently available size of RX buffer.
Finally, another issue of the distributed architecture is to achieve some kind of backward compatibility when building modular terminals, defining the interface between the modules, and above all concentrating on high speed.
In this connection, document US 2005/0111490 A1 discloses a communications bus having low latency interrupts and control signals, hotpluggability error detection and recovery, bandwidth allocation, network integrity verification, protocol tunneling and discoverability features. In detail, disclosed are methods and apparatus to control data and command flow over a physical communications channel between a transmitter and a receiver, and more specifically to provide a protocol for a point-to-point serial bus architecture with low latency time for flow control and other signaling, regardless of the length of the data packet frame. The abstract data flow control protocol can be employed by various buses as it interacts only with the lowest protocol layers. Separate buffers for data and control can be used to allow the bus to be compatible with slower buses also to support additional control functions without involving a higher protocol layer.